Harmful binge drinking occurs frequently on college campuses, undermining students' academic performance, social relationships, and somatic and mental health. Although research documents that counselor-delivered, brief motivational interventions (BMIs) reliably reduce drinking and related problems, the effects produced by BMIs tend to be small-to-medium in size and these effects are not always maintained, especially among students who have violated campus alcohol policies. Thus, to promote student health and safety, BMIs need to be improved to enhance the magnitude of the observed effects and maintain risk-reduction gains. In addition, to advance the science of health behavior change, research needs to improve understanding of the mechanisms by which brief interventions exert their beneficial impact. The proposed research will improve BMI-initiated change by developing a theoretically-guided, low-cost, e-mail booster (e-booster) to magnify and sustain the effects of BMI. The e-booster will be delivered using existing distribution technology between four to twelve weeks after the BMI (when beneficial effects begin to decay) and will target the hypothesized mechanisms of change; that is, e- booster messages will reinforce and expand upon the normative feedback component of the BMI and prompt peer discussion regarding normative data. The proposed research will be completed in two parts. Phase I will involve formative research to develop and refine e-booster and health behavior control messages with 200 student drinkers. Phase II will involve a randomized controlled trial (RCT) with 596 students referred for violating alcohol-related policy on campus. In this RCT, all referred students will receive a BMI, and then they will be randomized to one of two structurally-equivalent booster conditions: a) e-booster with corrective norms messages or b) a control series of health promotion e-mails. Students in both conditions will undergo a baseline assessment, receive a BMI, and return for follow-up assessments at 1, 3, 5, 8, and 12 months post-BMI. Key outcomes will be alcohol consumption and alcohol-related problems; hypothesized mediating variables will include descriptive and injunctive norms as well as peer communication. The proposed design will permit analyses that a) document initial BMI-induced changes; b) determine whether the e-booster enhances or maintains risk reduction over time; and c) test the hypothesized mediational mechanisms. This research will advance public health by providing a more powerful intervention for alcohol abuse prevention, and will advance prevention science by identifying social-cognitive mechanisms by which brief interventions change drinking behavior.